March 8, 1894J 



NA TURE 



447 



marked on the frontiers C'B and b'c, according to the form 

 mn ; and on the frontiers ba', ab', according to the 

 form uv. Fig. 4 was drawn on the same plan but with 

 one pair of frontiers left as straight lines, and the two 

 other pairs drawn by aid of two paper templets. It would be 



Fig. 



easy, but not worth the trouble, to cut out a large number of 

 pieces of brass of the shapes shown in these diagrams and to 

 show them fitted together like the pieces of a dissected map. 

 Figs. 5 and 6 are drawn on the same principle ; Fig. 6 showing, 



of solid space, the separating channels shown in Fig. 5 might 

 be sections, by the plane of the drawing, of perforations through 



Fig. s. 



the matter of one cell produced by the penetration of matter, 

 rootlets for example, from neighbouring cells. 



§ 9. Corresponding to the three ways by which two triangles 

 can be put together to make a parallelogram, there are seven, 



on a reduced scale, the result of putting pieces together pre- 

 cisely equal and similar to that shown in Fig. 5. In these 

 diagrams, unlike the cases represented in Figs. 3 and 4, the 

 primitive hexagon is, as shown clearly in Fig. 5, divided into 

 isolated parts. But if we are dealing with homogeneous division 



and only seven, ways in which the six tetrahedrons of § 4 can 

 be put together to make a parallelepiped, in positions parallel to 



NO. I 27 I, VOL. 49] 



